Journal of Geosciences, 62 (2017), 201–213

DOI: 10.3190/jgeosci.241

Original paper

Línekite, K2Ca3[(UO2)(CO3)3]2.8H2O, a new uranyl carbonate mineralfrom Jáchymov, Czech Republic
Jakub Plášil1*, Jiří Čejka2, Jiří Sejkora2, Jan Hloušek†, Radek Škoda3, Milan Novák3,
Michal Dušek1, Ivana Císařová4, Ivan Němec4, Jana Ederová5
Institute of Physics, Academy of Sciences of the Czech Republic v.v.i, Na Slovance 2, 182 21 Prague 8, Czech Republic; plasil@fzu.cz
Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Prague 9, Czech Republic†
Jáchymov; deceased on April 27, 20143
Department of Geological Sciences, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
4
Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 43 Prague 2, Czech Republic
5Institute of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic*
Corresponding author
1
2

Línekite, K2Ca3[(UO2)(CO3)3]2.8H2O, is a new uranyl tricarbonate mineral from Jáchymov, Western Bohemia, Czech
Republic. It occurs in association with grimselite, andersonite, liebigite, čejkaite, schröckingerite, agricolaite, ježekite
and braunerite. Línekite forms from uranium-rich aqueous solutions and its origin is associated with post-mining processes. Línekite is orthorhombic, space group Pnnm, with a = 17.0069(5) Å, b = 18.0273(5) Å, c = 18.3374(5) Å andV = 5622.1(2) Å3, and Z = 8. It forms tabular, mostly isometric crystals, up to c. 0.5 mm across, typically in multiple
intergrowths. The color is pale olive to khaki green and it has a greenish white to yellowish white streak. Crystals aretransparent and have vitreous luster. The Mohs hardness is estimated to be between 2 and 3. Línekite is brittle with anuneven fracture and perfect cleavage on {100} and very good cleavage on {010}. It exhibits intense greenish yellow
luminescence under both short- (254 nm) and long-wave (366 nm) UV radiation. The calculated density is 2.922 g/cm3.
The mineral is biaxial (+) with indices of refraction, α = 1.546(2), β = 1.550, γ = 1.562(2). The 2Vobs is moderate; thecalculated 2V is +60°. Optical orientation: Y = a, X = b, Z = c. The electron microprobe analyses (average of 28) provided:
Na2O 0.06, K2O 6.89, CaO 14.11, CuO 0.12, UO3 48.76, CO2* 22.51, H2O* 12.20 (~12.9 from TG) (*calculated), total
104.65 wt%. The empirical formula (based on 30.22 O apfu) is: (K1.73Na0.02)Σ1.75(Ca2.97Cu0.02)Σ2.99[(UO2)(CO3)3]2.02(H2O)8.00.
The Raman and infrared spectra exhibit prominent features consistent with the mineral being a hydrated uranyl tricarbonate, with fundamental vibrations of H2O molecules, CO32– anions and UO22+ ions. The seven strongest powder X‑ray
diffraction lines are [dobs in Å (hkl) Irel]: 8.627 (200) 100, 6.436 (022) 60, 5.935 (212) 11, 5.153 (222) 43, 4.592 (004)
19, 4.505 (040) 12 and 4.053 (204) 15. The structure of línekite was refined from single-crystal X-ray data to R = 0.034
for 4468 unique observed reflections (Iobs > 3σI). The structure consists of prominent (Ca(H2O)2[(UO2)(CO3)3])2– layers
parallel to (100), which define a square grid, leading to a strong tetragonal pseudosymmetry of línekite. Between thelayers, disordered K+ cations and H2O molecules are localized. The structure is closely related to other uranyl tricarbonate minerals, e.g., albrechtschraufite and andersonite, due to the presence of a very characteristic paddle-wheel motif,
Ca[(UO2)(CO3)3]4Ca.
Keywords: Línekite, uranyl carbonate, crystal structure, Raman spectroscopy, Jáchymov
Received: 11 June 2017; accepted: 21 August 2017; handling editor: F. Laufek
The online version of this article (doi: 10.3190/jgeosci.241) contains supplementary electronic material.

1. Introduction
Uranyl carbonate minerals are thermodynamically favored to precipitate from neutral- to alkaline aqueous solutions containing dissolved CO32– ions (Langmuir 1978).
The activity of carbonate species is usually maintained by
the dissolution of gangue carbonates, which are commonly associated with primary uraninite on most hydrothermal veins. Until recently the twenty-six uranyl carbonateshave been described as minerals (Krivovichev and Plášil
2013). The Jáchymov ore district is famous namely forthe occurrences of uranyl minerals, and among themuranyl carbonates have been of particular interest in thepast, as it is well documented e.g. by the early descriptionof the uranyl carbonate–sulfate mineral schröckingerite,
already in 1873 (Schrauf 1873; Mereiter 1986a). Several
remarkable uranyl carbonate minerals were describedfrom Jáchymov as their type locality; among them albrechtschraufite, MgCa4F2[(UO2)(CO3)3]2(H2O)17–18 (Mereiter 1984; 2013), čejkaite, Na4[(UO2)(CO3)3] (Ondruš
et al. 2003; Plášil et al. 2013) and agricolaite, K 4[(UO2)(CO3)3] (Skála et al. 2011). In this paper we provide thedescription of a new uranyl tricarbonate mineral from
Jáchymov, línekite, ideally K2Ca3[(UO2)(CO3)3]2.8H2O,
Strunz Class 05.ED, which is the first member containing
alkalis to alkaline earths in the ratio 2 : 3.
www.jgeosci.org

Jakub Plášil, Jiří Čejka, Jiří Sejkora, Jan Hloušek, Radek Škoda, Milan Novák, Michal Dušek, Ivana Císařová, Ivan Němec, Jana Ederová

Línekite is named in honor of Dr. Allan Línek (1925–
1984), a Czech physicist and crystallographer of theInstitute of Physics, Academy of Sciences of the Czech Republic, for his significant contribution to structure science.
The new mineral and its name have been approved by
the Commission on New Minerals, Nomenclature andClassification (CNMNC) of the International Mineralogical Association (IMA 2012–066). The description of themineral is based upon material from the holotype specimen, which is now depos­ited in the collections of the
Department of Mineralogy and Petrology of the National
Museum in Prague, Cirkusová 1740, Prague 9, Czech
Republic, catalog number P1P 2/2012.

2. Sample
Línekite was discovered in an old mine adit on the Geschieber vein, at the 5th level of the Svornost (Einigkeit)
mine, Jáchymov ore district, Western Bohemia, Czech
Republic. The mineral was found by one of the authors(JH) on the muddy or dusty surfaces of the surrounding
country rocks (dominantly dark amphibole schist) and,less commonly, also in gangue material lying as gravelon the footwall of the crossing-adit leading to the vein.
Liebigite, grimselite, andersonite, čejkaite, schröckingerite, agricolaite, ježekite (Plášil et al. 2015), braunerite (IMA 2015–123, Plášil et al. 2016), and gypsum
occur closely associated with línekite.
Since no primary uranium mineral or its relics were
found on the specimens, we conclude that the mineral
assemblage of uranyl carbonates and sulfates formed
from U-rich solutions, most probably containing uranyl–carbonate complexes that migrated from the primarysites. These solutions were likely alkaline or neutral. The
presence of (SO4)2– anions (in schröckingerite and inježekite) is due to abundance of pyrite in the associatedblack schist. The mineral assemblage in which línekite
occurs is typical of recent/subrecent association related
to post-mining processes.

3. Physical and optical properties
Línekite occurs as well-formed thin tabular crystals, up
to 0.5 mm in size, forming aggregates of sub-parallelintergrown crystals (Fig. 1). Their aggregates reach up to
1.2 mm across. Línekite crystals show a dominant {100}pinacoid form, and prism forms {101}, {110} and {011}(Fig. 2). The color is pale olive to khaki green. The streakis greenish white to yellowish white and luster is vitreous.
Línekite exhibits intense greenish yellow luminescence
under both short- (254 nm) and long-wave (366 nm) UV
radiation. The Mohs hardness ranges between 2 and 3.
The new mineral is brittle with uneven fracture and aperfect cleavage on {100} and a very good cleavage on{010}. The calculated density based on the empiricalformula is 2.922 g/cm3. The mineral is optically biaxial(+) with the following indices of refraction, measured
using 589 nm light: α = 1.546(2), β = 1.550, γ = 1.562(2).
The index β was measured only once due to the lack ofappropriately oriented crystal fragments. 2Vobs is moderate but the exact value could not be measured as theconoscopic figures were of a low quality; calculated 2V is+60°. Optical orientation: Y = a, X = b, Z = c. Línekite ispale khaki green and non-pleochroic in transmitted light.
It dissolves quickly in 10% HCl with the release of CO2
observed as bubbles.

4. Thermal analysis
A thermogravimetric study oflínekite (Fig. 3) was performed
on a Stanton Redcroft Thermobalance TG 750 in the range
20–900 °C, with a heating rateof 10 °C/min, in a dynamic
air atmosphere, a flow rate of
10 ml/min and a sample weightof 1.422 mg.
Thermal experiment documented that línekite dehydrates
in three distinct steps (Fig. 3;
Fig. 1 The aggregate of tabular línekite
crystals growing on the rock fragment.
Width of photograph 2 mm, photo by
Pavel Škácha.

202

Línekite, a new uranyl carbonate from Jáchymov

Fig. 2 The aggregate of línekite tabular
crystals. Secondary-electron image (JeolJSM–6370).

Electron microprobe analyses(28 representative points) were
performed at the Masaryk University in Brno using a Cameca
SX-100 electron microprobe(WDS mode, 15 kV, 2 nA,
15 μm beam diameter). The
following X-ray lines and standards were selected to minimize line overlaps; Kα lines: Ca(grossular), Cu (dioptase), Na
Fig. 3 Thermal gravimetry curves forlínekite.

weight loss (%)

5. Chemical composition(albite), K (sanidine); Mβ lines: U (metallic U). Other elements, including S, Si or Mg were also sought, but they
were not found (the detection limits of the analysis forthese elements are ~0.1 wt. % with the analytical conditions used). Peak counting times were 10–20 s and thecounting time for the background was 50 % of those on
the peak. The measured intensities were converted to elemental concentrations using the PAP program (Pouchou
and Pichoir 1985).
The results of electron microprobe analyses are summarized in Tab. 2. The empirical formula of línekite(based on 30.22 O apfu) is (K1.73Na0.02)Σ1.75(Ca2.97Cu0.02)Σ2.99
0.05

DTG

100

0.00

95

–0.05

90

–0.10

85

–0.15

80

–0.20

75

–0.25

TG

70

DTG (%/°C)

Tab. 1). Schematically, the whole process up to 413 °C
can be described as the release of 5 H2O (up to 125 °C), 2
H2O (between 125 and 188 °C), and 1 H2O and 1 CO2 (upto 413 °C) (Tab. 1). Some overlap of processes, dehydration and decarbonation, is possible. Additional CO2 molecules (3 CO2 and 2 CO2) are released up to 900 °C. The
full dehydration and carbon dioxide release are connectedwith the destruction of the línekite crystal structure. The
end-product of the thermal decomposition of línekite ismost probably (K,Ca)-uranate similar to the case of thermal decomposition of andersonite, when (Na,Ca)-uranate
is formed (Čejka 1969). The total content of molecularwater in línekite inferred fromthe thermal analysis is ~8 H2O
105(Tab. 1).

–0.30

65

–0.35
0

100

200

300

400

500

600

700

800

900

temperature (°C)

203

Jakub Plášil, Jiří Čejka, Jiří Sejkora, Jan Hloušek, Radek Škoda, Milan Novák, Michal Dušek, Ivana Císařová, Ivan Němec, Jana Ederová

cadmium–telluride detector)
was employed. A small amount
Temperature
Weight loss (wt. %)Mass units
Assignmentof the sample was pulverized
125
7.392
91.875
5 H2O (exp. 5.10 H2O)
and mixed with a portion of
188
3.113
38.6912 H2O (2.15 H2O)
KBr and immediately analyzed
413
3.941
48.983
1 H2O + 1 CO2 (0.76 H2O + 0.8 CO2)*
without preparation the pellet.
483
10.738133.463
3 CO2 (3.03 CO2)
900
7.675
95.3932 CO2 (2.17 CO2)
The same KBr without the spectotal
32.858408.405
8 H2O + 6 CO2 (8.01 H2O + 6 CO2)
imen was taken as the blank ref* data assigned tentatively
erence. Spectra were processed(background correction, fitting)using OMNIC Spectral tool software v.7.3 (Thermo[(UO 2)(CO 3) 3] 2.02(H 2O) 8. The basis of 30.22 O in the
Fisher Scientific Inc.). The Raman and infrared spectra
calculation was chosen due to charge balance. The idealof línekite are interpreted with regard to the papers byformula of línekite is K2Ca3[(UO2)(CO3)3]2.8H2O, which
Koglin et al. (1979), Anderson et al. (1980), and Čejka
requires K2O 7.58, CaO 13.54, CO2 21.25, UO3 46.03,(1999, 2005).
H 2O 11.60, total 100.00 wt. %. The Gladstone-Dalecompatibility index 1–(KP/KC) is –0.001 for the empiricalformula, indicating a superior compatibility (Mandarino
6.1. O–H vibrations
1981).
Tab. 1 Thermal analysis of línekite

6. Raman and infrared spectroscopy
The Raman spectrum (Fig. 4) of línekite was collectedusing a DXR dispersive Raman spectrometer (Thermo
Scientific) mounted on a confocal Olympus microscope(100× objective). The Raman signal was excited by a 532
nm diode-pumped solid-state laser and then detected by a
CCD detector. Experimental parameters: exposure time,
10 s; number of exposures, 32; grating, 400 lines/mm;
spectrograph aperture, 50 µm slit; camera temperature,–50 °C; laser power level, 3.0 mW. The instrument wascalibrated by a software-controlled calibration procedureusing multiple neon emission lines (wavelength calibration), multiple polystyrene Raman bands (laser frequency
calibration) and standardized white light sources (intensity calibration). For acquiring the infrared spectrumof línekite (Fig. 5), a micro diffuse reflectance infrared
Fourier transform spectroscopy (micro-DRIFTS) was
utilized. The Thermo Nicolet 6700 FTIR spectrometer(range 4000–600 cm –1, resolution 4 cm –1, 128 scans,
Happ–Genzel apodization) equipped with a Spectra Tech
InspectIR Plus micro-spectroscopic accessory (mercury–
Tab. 2 Chemical composition of línekite
Constituent
Na2O
K 2O
CaO
CuO
CO2*
UO3
H2O*

Mean of 28 points (wt. %)RangeStand. Dev.
0.06
0.00–0.28
0.07
6.89
6.53–7.34
0.21
14.11
13.28–14.78
0.35
0.12
0.00–0.53
0.18
22.51
48.76
47.63–50.04
0.59
12.20

Total
104.65*Contents of H2O* and CO2* were calculated from stoichiometry
derived from the thermal analysis

204

The Raman and infrared bands and shoulders in the region above 2500 cm–1 (Raman bands at 3500, 3470, 3270,
3080, 2900 and 2740 cm–1 and infrared bands and shoulders at 3590, 3500, 3380, 3220, 3010, 2730 and 2570
cm–1) were assigned to ν O–H stretching frequencies ofstructurally non-equivalent (symmetrically distinct) H 2O
molecules bonded in the structure by the network of Hbonds. According to the empirical relation provided by
Libowitzky (1999), the O⋅⋅⋅O separation distances of thehydrogen bonds vary approximately between 2.9 and 2.6
Å (based on Raman) or between 3.2 and 2.6 Å (basedon infrared). A band observed in the Raman spectrum
at 1667 cm–1 and infrared bands and shoulders at 1698,
1654 and 1609 cm–1 are attributed to the ν2 (δ) bending
vibrations of symmetrically distinct H2O molecules. The
weak infrared bands at 788 and at 623 cm–1 may be connected with libration modes of H2O.

6.2. CO32– vibrations
Raman bands and shoulders at 1590, 1564, 1392 and
1346 cm–1 and infrared bands at 1580, 1553, 1522, 1389
and 1364 cm –1 are attributed to the ν3 antisymmetricstretching vibrations of structurally nonequivalent CO3
planar groups. The observed splitting of the ν 3 bands
indicates the presence of bidentately bonded carbonate
groups onto uranyl hexagonal bipyramids in the crystal
structure.
Raman bands and shoulders at 1095, 1085 and 1070
cm–1 and infrared band at 1069 cm–1 were assigned to theν1 symmetric stretching vibration of the CO3 groups. The
Raman band at 836 cm–1 and infrared bands at 853 and833 cm–1 are attributed to the 2 (δ) out-of-plane bending
vibration of CO3. Some overlap of the ν2 (δ) CO3 bending vibration with the ν1 UO22+ symmetric stretchingvibration can be expected. Raman bands and shouldersLínekite, a new uranyl carbonate from Jáchymov

Raman Intensity (a.u.)~

lattice
modes

3000

Fig. 4 Raman spectrum of línekite.

2000

at 750, 735, 704 and 680 cm–1 and infrared bands at 752,
738, 694 and 658 cm–1 are assigned to the ν4 (δ) in-planebending CO3 vibration.

6.3. Vibrations of UO22+

1000

500

100

7. X-ray crystallography and crystal
structure
Powder x-ray diffraction data of línekite were collectedfrom a capillary sample in Debye-Scherrer geometry
using a PANalytical Empyrean powder diffractometerequipped with a Cu X‑ray tube (45 kV, 40 mA), PIXcel3D solid-state detector and primary focusing Göbel
mirror optics. The powder pattern was measured from
3 to 80° 2θ with a step size 0.013° 2θ and a counting
time 1 s per step. The repeated scan option was utilized

Kubelka-Munk

The Raman band at 822 cm–1 and infrared band at 809
cm–1 belong to the ν1 symmetric stretching mode of UO22+
and an infrared band at 892 cm–1 to the ν3 antisymmetricstretching mode of UO22+. As noted above, some overlap
with the ν2 of CO3 cannot be excluded. According to therelation provided by Bartlett
and Cooney (1989), U–O bondlengths inferred from the wavenumbers of uranyl stretchingvibrations vary in the range of
1.78–1.80 Å. Those values arein agreement with the values
given by Burns et al. (1997)
for uranyl ions coordinated inhexagonal bipyramids. The Raman bands at 339, 324 and 298
cm –1 may be related to the ν(U–Oligand) stretching vibrations
and those bands at 249 and 236
cm–1 are connected with the ν2(δ) bends of uranyl. However,some overlaps may be expectedin this spectral region. Bands at
the lowest wavenumbers wereassigned to lattice modes.
4000

Fig. 5 The infrared spectrum of línekite.

1500

Raman shift (cm–1)

3500

CO2 artifact

3000

2500

2000

1500

1000

Wavenumbers (cm–1)
205

Jakub Plášil, Jiří Čejka, Jiří Sejkora, Jan Hloušek, Radek Škoda, Milan Novák, Michal Dušek, Ivana Císařová, Ivan Němec, Jana Ederová

Tab. 3 Powder X-ray diffraction data (dhkl in Å) for línekite
Irel

dobs

1
10.306
1
9.186
100
8.627
60
6.436
4
6.231
9
6.028
11
5.935
2
5.712
8
5.492
3
5.422
43
5.153
5
4.932
1
4.858
1
4.710
19
4.592
12
4.505
8
4.360
6
4.311
5
4.195
3
4.153
5
4.083
15
4.053
10
3.996
5
3.953
4
3.903
5
3.813
3
3.786
2
3.703
11
3.583
4
3.549
4
3.525
7
3.504
4
3.480
1
3.392
2
3.339
4
3.275
4
3.218
1
3.163
3
3.144
3
3.118
8
3.097
4
3.061
2
3.044
4
3.015
1
2.992
2
2.963
1
2.955
1
2.926
5
2.900
1
2.877
5
2.862
7
2.853
5
2.843
8
2.820
d values quoted in Å

206

Línekite (this paper)
dcalc
Icalc
10.316
9.183
8.627
6.435
6.234
6.029
5.937
5.715
5.495
5.425
5.158
4.933
4.860
4.689
4.591
4.510
4.346
4.313
4.195
4.163
4.083
4.053
3.997
3.954
3.904
3.816
3.801
3.697
3.583
3.549
3.523
3.505
3.484
3.391
3.338
3.274
3.217
3.163
3.144
3.117
3.097
3.061
3.051
3.015
2.993
2.962
2.952
2.924
2.899
2.885
2.857
2.852
2.849
2.819

2
3
100
84
7
3
21
2
16
9
98
11
2
<1
30
23
2
5
5
<1
4
22
20
8
4
8
5
2
27
2
6
16
3
2
1
5
9
1
6
12
9
3
2
9
<1
1
1
1
10
1
10
7
4
3

h

k

l

1
0
2
0
2
1
2
0
1
1
2
2
1
3
0
0
2
4
4
1
3
2
2
2
4
4
3
2
4
3
1
4
3
5
1
4
0
1
4
4
4
0
3
2
5
1
4
1
0
2
0
5
2
1

1
0
0
2
2
2
1
3
1
3
2
3
2
2
0
4
3
0
1
3
1
0
4
1
0
1
2
2
2
4
1
3
4
0
2
3
4
4
0
4
1
0
1
4
3
6
4
6
2
0
6
2
1
6

1
2
0
2
0
2
2
1
3
1
2
0
3
1
4
0
2
0
0
3
3
4
0
4
2
2
3
4
2
0
5
0
1
1
5
2
4
4
4
0
4
6
5
4
0
0
2
1
6
6
2
3
6
2

Meyrowitz et al. (1964)
dobs
Irel

8.70
6.40
6.25
6.03
5.95
5.73
5.50
5.43
5.17
4.94

100
36
4
7
13
4
11
4
46
6

4.60
4.51
4.37
4.32
4.21
4.17

31
11
11
20
14
4

4.06
4.00

24
11

to improve the counting statistics with an accumulation of
40 scans. Before the measurement, the diffractometer wascalibrated against a LaB6 capillary standard. Positions of thediffraction peaks were refinedusing the pseudo-Voigt profile
function using least-squares ofthe High-Score Plus program(PANalytical). The unit cell parameters were refined from thepowder data by Celref program(Laugier and Bochu 2014) using the diffraction peaks up to
45 °2θ (99 diffractions). The
hkl indices were taken fromthe calculated powder diffraction pattern obtained from thePowderCell program (Kraus andNolze 1996). The refined unitcell parameters of línekite are:a = 17.254(4) Å, b = 18.040(4) Å,c = 18.366(4) Å and V = 5717(2)Å3. The powder data for línekite
are listed in Tab. 3.
A 0.31 × 0.25 × 0.11 mm large
green crystal of línekite wasselected for the single-crystal
X-ray diffraction experimentusing an Oxford diffraction
Gemini single-crystal diffractometer, with monochromated
MoKα radiation (λ = 0.71073 Å;
55 kV, 38 mA) from a sealed
X-ray tube monochromatizedwith a graphite monochromator, collimated with a fiberoptics Mo-Enhance collimator,and detected with an a Atlas
CCD detector. The best crystal
selected for the diffraction experiment was, however, foundto be a split crystal with partially overlapping reflections. A
twin-matrix for determining theoverlaps of partially and fully
separated reflections was later
used in the refinement of thestructure. The crystallographic
details with the parameters forthe data collection and refinement are listed in Tab. 4. The
intensity data were correctedLínekite, a new uranyl carbonate from Jáchymov

for Lorentz factor, polarization Tab. 3 Continued
and background. The absorption
Línekite (this paper)
Meyrowitz et al. (1964)
correction, combining numeri- I
h
k
l
dobs
dobs
dcalc
Icalc
Irel
rel
cal shape-based correction and
3
2.812
2.810
2
1
4
5
the empirical scaling, was done
1
2.803
2.808
1
3
4
4
in Jana2006 software (Petříček
4
2.786
2.786
3
4
3
4
et al. 2014), leading to the Rint
9
2.749
2.748
12
2
2
6
= 0.046.
4
2.745
2.744
3
6
0
2
The structure of línekite was
1
2.729
2.734
3
3
5
3
solved independently from the
4
2.712
2.712
11
2
6
2
known structure of the synthetic
2
2.691
2.689
3
5
3
3
1
2.652
2.650
4
4
5
2
phase (Hughes-Kubatko and
2
2.580
2.579
12
4
4
4
Burns 2004). The refinement of
3
2.560
2.559
2
3
6
2
that model in Jana2006 software
2
2.554
2.552
1
3
4
5
(Petříček et al. 2014), using our
<1
2.545
2.546
<1
1
5
5
dataset, led only to the less1
2.525
2.525
3
1
7
1
satisfactory results, correspond4
2.498
2.496
3
6
3
2
ing to higher residuals: the
1
2.491
2.493
2
1
2
7
R ([I obs >3σ(I)]) = 0.049 and
1
2.469
2.471
2
5
5
1
wR (([Iobs>3σ(I)]) = 0.119 with
1
2.422
2.423
<1
5
2
5
GOF = 2.15; maximal and mini2
2.416
2.415
2
6
1
4
mal peaks in the difference3
2.407
2.406
5
4
2
6
Fourier electron-density were
2
2.382
2.382
5
4
6
2
4.93 and –2.53 e Å–3. Therefore
4
2.369
2.366
7
3
1
7
a new structure solution was
3
2.347
2.344
2
6
4
2
carried out using SIR2002 soft2
2.309
2.308
4
3
2
7
ware (Burla et al. 2003) in the
1
2.296
2.296
2
0
0
8
space group Pnnm, which was
2
2.220
2.218
2
2
0
8
1
2.213
2.212
5
4
7
0
chosen based on the reflection
2
2.198
2.197
4
5
4
5
conditions. The model obtained
1
2.185
2.184
1
4
4
6
was subsequently refined in
2
2.150
2.151
2
4
7
2
Jana2006 using a full-matrix
1
2.143
2.144
1
6
4
4
least-squares algorithm based
1
2.124
2.126
2
5
6
3
2
on F employed therein. The
3
2.108
2.106
5
1
5
7
refinement confirmed that the
5
2.094
2.094
3
1
7
5
structure of línekite is extremely
3
2.083
2.082
2
6
1
6
pseudosymmetric and contains a
1
2.077
2.078
2
6
6
0
high degree of disorder, involv2
2.065
2.065
1
5
7
0
ing especially disordered C, O
2
2.061
2.063
1
5
5
5
sites (of the H 2O molecules),
4
2.035
2.035
7
5
2
7
and K sites, with considerably
3
2.029
2.030
1
8
3
0
lowered occupations of the cor2
2.023
2.024
2
0
8
4
responding sites. That disorder
2
2.012
2.014
1
1
1
9
corresponds to larger differences2
1.9933
1.99302474
between línkeite structure and31.98991.9907535
71
1.97881.97941
1
91
the structure of the synthetic
phase, which is also responsible d values quoted in Åfor the less accuracy of thee Å–3. Refined atom coordinates, displacement paramrefinement while using the structure of synthetics as aeters, and occupation factors are given in Tab. 5. The
starting model for the least-squares refinement. The finalbond-valence analysis of the structure was carried out
cycle of the refinement converged with the residuals R
following the procedure of Brown (1981, 2002), based([Iobs>3σ(I)]) = 0.0340 and wR ([Iobs>3σ(I)]) = 0.0783
on the refined interatomic distances (Electronic Supplewith GOF = 1.82; maximal and minimal peaks in thementary Material 1), and is provided in the Electronic
difference-Fourier electron-density were 3.00 and –1.12
207

Jakub Plášil, Jiří Čejka, Jiří Sejkora, Jan Hloušek, Radek Škoda, Milan Novák, Michal Dušek, Ivana Císařová, Ivan Němec, Jana Ederová

attached bidentately to the bipyramid
to form the uranyl tricarbonate clusCrystal datater, [(UO2)(CO3)3]4–. There are four
FormulaK1.952Ca3[(UO2)(CO3)3]2(H2O)7.164
disordered (split) CO3 groups, C5 and
Crystal system
orthorhombic
C5’, C7 and C7’, linked to the U2 andSpace groupPnnm
U3 hexagonal bipyramids. The uranyl
Unit-cell parameters: a, b, c [Å]
17.0069(5), 18.0273(5), 18.3374(5)Unit-cell volume [Å3]5622.0(3)tricarbonate clusters are not attachedZ8
directly to each other, but through the
Calculated density [g/cm3]
2.904 (for the above given formula)
Ca–O bonds they are connected into
Crystal size [mm]0.31 × 0.25 × 0.11
sheets stacked perpendicular to a.
The four sites, occupied by Ca2+, areData collection
coordinated in a distinct way in the
Diffractometer
Oxford Diffraction Gemini with Atlas detector
línekite structure (Fig. 6). The Ca1
Temperature [K]300
site is coordinated by seven ligands
Radiation, wavelength [Å]MoKα, 0.71073 (50 kV, 30 mA)
including one H 2O group (O26w)
θ range for data collection [º]2.7728.40
linked to the four U6+ sites. The Ca2Limiting Miller indicesh = –15→21, k = –23→20, l = –23 → 23
site is also linked to the four U6+
Axis, frame width (º), time per frame (s)ω, 1.0, 100
sites (symmetrically related U1 sites,
Total reflections collected
34219
U2 and U3), coordinated by seven
Unique reflections
6179
ligands, including one H 2O group
Unique observed reflections, criterion
4468, [I > 3σ(I)](O27w), linking the K5 site. The Ca3
Absorption coefficient [mm–1], type12.942, multi-scansite is located at the mirror plane
0.097/0.344
Tmin/Tmax
and is coordinated by the six ligands
0.046
Rint
4405
F000
(three of them are split sites), linked
to the four U6+ sites (symmetrically2
Structure refinement by Jana2006
Full-matrix least-squares on F
related U1 sites, U2 and U3). Among
No. of ref. param., restraints, constraints
429, 0, 6
the ligands linked to the Ca3 site weR, wR (obs)0.0339, 0.0782
can observe increased disorder maniR, wR (all)0.0545, 0.0839
fested in large thermal parameters
GOF obs/all
1.82, 1.64
for the O24/O24’, O27w/O27w’, andWeighting scheme, weights
σ, w =1/(σ2(I) + 0.0004I2)
O31w/O31w’ atoms, modeled in the–1.26, 3.61
Largest diff. peak and hole (e–/Å3)
current refinement as the split sites.
Twin fractions
0.93(1), 0.07(1)Finally, the Ca4 site is linked only
- 0.02 - 0.04 
 1
to a single U site (U3) via symmetri
10 
Twin matrix
 0.03cally related O22 atom and further
 0.050
1 coordinated by seven ligands, including positionally disordered H2O
Supplementary Material 2. Moreover, the CIF file, also
molecules (O31w and O31w’, modeled as split-sites).
containing a block with the reflections, is deposited at the
All Ca2+ sites were found to be fully occupied. Linkage
Journal’s web page www.jgeosci.org.
of the uranyl tricarbonate clusters and Ca 2+ polyhedra
results in the sheets, stacked along (100), which are themost rigid part of the línekite structure. The basic unit
7.1. Crystal structureof these compact regions in the structure is a cluster werefer to as paddle-wheel structure, where two Ca2+ (Ca1
There are three U6+ sites, nine C4+ sites (including two
and Ca2) are linked via four CO3 groups of four distinct
split-sites; positionally disordered from their correspond[(UO2)(CO3)3]4– clusters (Fig. 6). In línekite, each uranyl
ing special positions at the mirror planes), four Ca2+ sites,
tricarbonate cluster is a part of two paddle-wheels (Fig.
six K+ sites and thirty-seven O sites (including split-sites),7) that link them into a square-grid (Fig. 8a), composed
eleven of which are occupied by the molecular H2O.
of the orthorhombic-distorted tetragonal Ca2(H2O)2[(UO2)
The three independent U6+ sites are each coordinated by(CO3)3]2 layers, leading to strongly pseudo-tetragonal
two, strongly bonded O atoms at the distance of ~1.8 Å
diffraction pattern (Fig. 8b). The paddle-wheel motif(Electronic Supplementary Material 1), forming uranyl
is characteristic of related uranyl carbonate minerals
ions, UO22+. These are in turn further coordinated by six O
and compounds (Vochten et al. 1994; Mereiter 1986b;
atoms, arranged at the equatorial vertices of hexagonal biHughes-Kubatko and Burns 2004; Mereiter 2013).
pyramids. Each bipyramid is chelated by three CO3 groups
Tab. 4 Data collection and structure refinement for línekite

208

U1
U2
U3
Ca1
Ca2
Ca3
Ca4
K1
K2
K3
K4
K5
K6
C1
C2
C3
C4
C5
C5’
C6
C7
C7’
O1
O2
O3
O4
O5
O6
O7
O8
O9
O10
O11
O12
O13
O14
O15
O16
O17
O18
O19

0.5
0.5

0.5
0.5

0.778(10)0.874(19)0.338(14)0.443(13)0.243(11)0.31(2)Occ.

0.207596(15)0.76697(2)0.76647(2)0.32298(8)0.32491(8)0.46676(13)0.06448(14)−0.02733(18)00.5437(7)0.2198(4)0.5378(6)0.7138(9)0.1386(5)0.3587(4)0.3621(4)0.3322(5)0.3476(14)0.3680(14)0.1719(4)0.3597(14)0.3291(13)0.1595(3)0.2555(3)0.2982(3)0.397(3)0.1038(3)0.3193(3)0.2063(3)0.3225(3)0.6991(5)0.8348(5)0.3289(3)0.3581(3)0.2733(3)0.6911(5)0.8415(5)0.1505(3)0.3216(4)0.2280(3)0.1097(3)x/a0.239027(14)0.48990(2)0.02820(2)0.42930(8)0.04955(8)0.24034(11)−0.18296(12)0.2292(2)0.50.4529(8)0.2742(4)0.0291(6)0.2547(9)0.1000(4)0.2398(4)−0.1229(4)0.0553(4)0.3956(14)0.4072(13)−0.0832(4)0.0773(12)0.1053(13)0.2374(3)0.2404(3)−0.1261(3)−0.1861(3)0.1621(3)0.2998(3)0.1037(3)0.1799(3)0.4139(4)0.5663(4)0.4308(3)0.0794(3)0.0121(3)0.0963(5)−0.0421(4)−0.1079(3)0.0579(4)−0.0343(3)0.0402(3)y/b0.225854(15)000.18733(8)0.18639(8)000.21506(17)0−0.0601(6)00.0395(6)00.2634(4)0.1546(4)0.2333(5)0.3637(4)000.1360(4)000.1396(3)0.3115(3)0.2702(3)0.2237(3)0.2721(3)0.1677(3)0.2313(3)0.1733(3)000.0590(3)0.4269(3)0.3663(3)000.0715(3)0.0591(3)0.1329(3)0.2864(3)z/c0.02236(9)0.02423(14)0.02529(14)0.0210(5)0.0206(5)0.0267(7)0.0328(8)0.0667(14)0.073(3)0.148(7)0.049(3)0.067(4)0.118(10)0.028(3)0.025(2)0.029(3)0.029(3)0.022(3)*0.022(3)*0.024(2)0.027(4)*0.027(4)*0.039(2)0.038(2)0.0301(18)0.0355(19)0.040(2)0.037(2)0.0309(18)0.038(2)0.040(3)0.038(3)0.038(2)0.036(2)0.0332(19)0.042(3)0.043(3)0.0320(19)0.052(2)0.0323(19)0.036(2)Uiso/Ueq

0.044(4)0.041(3)0.028(3)0.033(3)0.036(3)0.042(3)0.031(3)0.037(3)0.037(5)0.040(5)0.056(4)0.039(4)0.042(4)0.041(5)0.043(6)0.043(4)0.064(5)0.036(4)0.030(3)0.027(4)0.02471(15)0.0306(2)0.0291(2)0.0246(8)0.0260(8)0.0358(13)0.0336(14)0.050(2)0.043(4)0.143(12)0.050(5)0.054(8)0.076(13)0.031(5)0.029(4)0.023(4)0.035(5)

U11

Tab. 5 Atom site occupancies, coordinates and displacement parameters (Uiso/Ueq/Uaniso, in Å2) for línkeite
U220.039(3)0.039(3)0.022(3)0.020(3)0.020(3)0.017(3)0.020(3)0.017(3)0.026(4)0.039(5)0.045(4)0.047(3)0.038(3)0.047(5)0.034(5)0.037(3)0.072(5)0.037(3)0.025(3)0.027(4)0.01780(13)0.0246(2)0.0290(2)0.0192(7)0.0175(7)0.0223(10)0.0309(12)0.103(3)0.117(6)0.175(12)0.060(5)0.060(7)0.092(13)0.019(4)0.025(4)0.025(4)0.030(4)U33

0.033(3)0.033(4)0.040(4)0.054(4)0.063(4)0.053(4)0.042(4)0.060(4)0.055(6)0.036(5)0.014(3)0.020(3)0.019(3)0.037(5)0.053(6)0.016(3)0.020(3)0.023(3)0.053(4)0.019(5)0.02457(17)0.0176(2)0.0178(2)0.0192(9)0.0182(8)0.0220(12)0.0338(14)0.046(2)0.059(5)0.126(11)0.037(5)0.087(8)0.19(2)0.035(5)0.022(4)0.039(5)0.021(5)U12−0.005(3)0.001(3)0.001(2)0.000(2)0.005(2)−0.001(2)−0.001(2)0.003(2)−0.003(3)−0.001(4)0.024(3)−0.022(3)−0.015(2)0.004(4)−0.001(4)−0.015(2)−0.045(4)−0.016(2)−0.003(2)−0.003(3)0.00021(10)0.00595(15)−0.00855(16)0.0013(5)−0.0004(5)−0.0003(9)−0.0067(9)−0.0096(17)−0.002(3)−0.123(9)−0.001(3)0.021(4)−0.009(8)0.001(3)0.003(3)0.000(3)−0.008(3)U13−0.004(3)0.002(3)0.013(2)0.015(3)0.020(3)0.025(3)0.014(3)0.025(3)000.004(3)0.000(2)−0.003(2)00−0.002(2)−0.003(3)−0.001(2)0.008(3)0.001(3)0.00438(10)000.0010(6)0.0012(6)00−0.0039(13)0−0.056(7)00.025(5)00.003(3)0.003(3)0.004(3)0.002(3)U23−0.001(3)0.002(3)−0.002(3)0.009(3)0.008(3)−0.001(3)0.001(2)0.004(3)000.000(3)−0.002(3)0.001(3)00−0.002(2)0.003(3)−0.004(3)0.012(3)0.002(3)−0.00057(12)00−0.0003(6)0.0004(6)00−0.0151(17)00.059(8)00.011(5)00.003(4)0.002(3)0.003(4)0.005(4)

Línekite, a new uranyl carbonate from Jáchymov

209

210

0
0.015(3)0.015(3)00.005(3)0.000(3)−0.013(4)0.010(3)−0.003(2)0.066(6)0.070(4)0.042(3)0.037(6)0.031(4)0.027(3)0.057(7)0.044(4)0.050(4)0.006(3)−0.066(7)0−0.024(4)0.027(5)0−0.003(3)−0.022(5)−0.036(6)0.039(4)0.124(8)0.077(7)0.072(5)0.075(6)0.069(8)0.056(5)0.114(8)0.085(8)0.005(3)0.007(3)−0.004(3)0.001(2)0.005(2)0.015(3)0.002(3)0.009(2)−0.009(3)0.000(2)−0.014(3)0.001(2)0.018(3)0.060 (4)0.01(3)0.030(3)0.045(3)0.021(3)0.053(4)0.029(3)0.041(4)0.030(3)0.049(4)0.027(3)O20
0.1389(3)−0.1032(3)0.1931(3)0.0344(19)O210.3901(3)−0.0637(3)0.2082(3)0.037(2)O22
0.3658(3)0.0747(3)0.3062(3)0.040(2)O23
0.4266(3)0.2398(3)0.1285(3)0.0289(17)O24
0.5
0.4228(10)0.3654(9)00.035(3)*O24’ 0.5
0.3862(10)0.3392(9)00.035(3)*O25
0.5
0.4168(9)0.1213(8)00.035(3)*O26
0.5
0.3493(9)0.1683(8)00.035(3)*O27w 0.5
0.5771(10)0.2651(9)0.0765(9)0.073(3)*O27w’ 0.5
0.5787(9)0.2060(10)0.0771(8)0.073(3)*O28w
0.1215(4)−0.2695(3)0.0850(4)0.055(3)O29w−0.0239(5)−0.1373(6)0.0919(5)0.105(4)O30w−0.0375(6)−0.2799(6)00.077(5)O31w 0.760(13)0.0306(7)0.3891(7)0.1207(7)0.100(4)*O31w’ 0.240(13)0.008(3)0.478(2)0.1552(19)0.100(4)*O32w 0.17(3)0.006(2)0.067(2)0.035(2)0.06(2)*
O33w
0.5
0.5
0.3351(5)0.053(4)O34w
0.4598(3)0.3989(4)−0.1643(3)0.048(2)O35w
0.4609(3)0.0825(3)0.1588(3)0.040(2)’ – split site; w – H2O site; * − refined with isotropic atomic displacement parameters

Occ.

Tab. 5 Continued

x/a

y/b

z/c

Uiso/Ueq

U11

U22

U33

U12

U13

U23

Jakub Plášil, Jiří Čejka, Jiří Sejkora, Jan Hloušek, Radek Škoda, Milan Novák, Michal Dušek, Ivana Císařová, Ivan Němec, Jana Ederová

There are six sites in the structure of línekite, occupied
by K+ cations. All sites have reduced occupancies, as
documented from the site-scattering, varying from ~85%
to ~25% site-occupancy. Hydrated potassium cations
represent the least firm part of the structure. The refinement K and O atoms (of the H2O groups) is particularly
difficult due to driven pseudosymmetry of just slightly
orthorhombic-distorted tetragonal Ca 2 (H 2 O) 2 [(UO 2 )(CO3)3]2 layers. The assignment of whether the site isdominantly occupied by H2O and/or K+, is conclusively
not straightforward in the case of línekite. Here in caseof such pseudosymmetry, the fact that K–O bond lengths
are similar to the O…O distances for the hydrogen-bonded
H2O molecules makes the entire issue difficult. The current approach resulting in the presented structure model isbased on the fact that disordered K or Ca atoms still tend
to provide sharper Fourier peaks than the disordered H2O
molecules. The effect of pseudosymmetry in línekite canbe demonstrated on the K2 site and its coordination environment in particular. The K2 sitting on a mirror plane
is coordinated by fourteen ligands, among them, eight aresymmetrically related split atom sites (O32w, O32w’).
We can also view it as that the K2 coordination polyhedra
are squeezed between two paddle-wheel structures, which
can induce such disorder in coordinated, partly occupied
H2O sites. The final content of K+ per unit cell obtained
from the site-scattering refinement is 1.952 atoms, which
is nearly the ideal stoichiometric content.
The eleven O sites in línekite structure, including
split-sites, belong to the molecular H2O, according to
the bond-valence analysis (Electronic Supplementary
Material 2) and the coordination scheme. Except for
O34w atom, located in the cavity of the framework, allother O sites occupied by H2O molecules are coordinatedto Ca2+ and namely to K+ cations. The majority of H2O
molecules in the structure are positionally disordered
and have also a considerably lowered occupation. The
phenomenon mentioned above is driven again by thestrong pseudosymmetry of Ca 2(H 2O) 2[(UO 2)(CO 3) 3] 2
layers where no desymmetrization takes place. The only
ordered and fully occupied H2O sites are coordinated toCa2+ cations within the layers. The refinement of the Osite occupancies, associated with the H2O sites, yielded
the sum of 7.164 H2O per the unit cell.

8. Discussion – relationship to thesynthetic analogs and other uranyl
carbonates, the stoichiometry and thewater content of línekite
Línekite, the synthetic phase prepared by Meyrowitz etal. (1964) and the synthetics by Hughes-Kubatko andBurns (2004) are essentially isostructural. The synthetic

Línekite, a new uranyl carbonate from Jáchymov

Fig. 6 The (100) sheet of the nominal composition {Ca3[(UO)2(CO3)3]2}2– in the structureof línekite. The red dashed eclipse marks the“paddle-wheel” motif. Each uranyl tricarbonate
cluster is involved in the two “paddle-wheels”.

phase prepared by Meyrowitz et al. (1964) has a unitcell of the dimensions a = 17.98, b = 18.29, c = 16.95 Å;
space groups inferred Pnmn or Pn2n. The powder data
provided by Meyrowitz et al. (1964) fit very well to thediffraction data of línekite (Tab. 2) and the indices of refraction are also in the range, α = 1.544(3), β = 1.549(3),γ = 1.5′63(3).
The cationic content in theformula of línekite obtained
from the structure refinement,
K 1.952Ca 3[(UO 2)(CO 3) 3] 2(H 2O) 7.165(Z = 8), is close to the ideal stoichiometry K:Ca = 2:3. The resultsof electron microprobe analysis,
however, gave a lower K+ content,(K 1.73 Na 0.02 ) Σ1.75 (Ca 2.97 Cu 0.02 ) Σ2.99 .
This not unreasonable, due to theoverlap of K Kα and U Kα peaksin the spectrum and consequent
problems while measuring exact
concentrations of K, even in the
WDS mode. We are convinced thatthe cationic content in línekite issimilar to the other related uranyl

tricarbonates containing alkali- or earth-alkaline cations(Mereiter 1986a, b, 2013), showing no departures fromthe ideal stoichiometry. It is possible that a small amountof excessing Ca2+ cations could also entry the K sites
in the structure; however, this is not the case. The only
known non-stoichiometric exception among uranyl tricarbonates is a synthetic phase of Vochten et al. (1994),

Fig. 7 The “paddle-wheel” in línekite
structure, where the two Ca2+ cations takepart in linkage to four uranyl tricarbonate
clusters. The Ca1–Ca2 distance is 4.05 Å.
Captions to abbreviations: Ur – apical O
atom of the UO22+ ion; eq – equatorial O
atom of the UO8; OXc – O atom no. X of
the CO3 group; w – H2O site; ′ – split site.

211

Jakub Plášil, Jiří Čejka, Jiří Sejkora, Jan Hloušek, Radek Škoda, Milan Novák, Michal Dušek, Ivana Císařová, Ivan Němec, Jana Ederová

Fig. 8 The square grid of the (100) sheet in the structure of línkeite (a) leading to the strongly pseudo-tetragonal diffraction pattern (b). The latter
was calculated by Jana2006 as Fcalc for the contributions of the U and Ca atoms only.

Ca 1.54 Na 0.63 [(UO 2 )(CO 3 ) 3 ](H 2 O) ~5.38 . This compound,noteworthy, has a similar unit-cell metrics as línekite(a = 18.2, b = 16.9, c = 18.4 Å, Z = 8, space group:Pnnm). Línekite has an extremely pseudosymmetricstructure and a high degree of disorder; consequently,
the structure refinement is problematic. The content ofmolecular H2O both in línekite and in the synthetic analog
by Hughes-Kubatko and Burns (2004), obtained fromthe refinement of single-crystal X-ray data only, is thus
underestimated. The only reliable values can be obtained
from the chemical analysis (thermogravimetric or gas/
vapor-absorption measurement in a combustion train) in
the case of such a high-degree disorder as present in the
structure of línekite (since no desymmetrization takes
place there).
Acknowledgements. The authors thank Ladislav Lapčák(Institute of Chemical Technology, Prague) for the collection of the Raman spectrum of línekite and Karla
Fejfarová (BIOCEV, Prague) for help with X-ray datacollection. Kurt Mereiter (TU Vienna) is highly acknowledged for the discussion on the línekite, a thorough critical reading of the manuscript and reviews on the earlier
versions of the text. Comments by František Veselovský
and an anonymous referee as well as handling editor
František Laufek helped in improving the manuscript.
This research was financially supported the project No.
LO1603 under the Ministry of Education, Youth andSports National sustainability program I of Czech Republic to JP, MD and by the long-term project DKRVO
2017-01 of the Ministry of Culture of the Czech Republic(National Museum 000232782) to JS and JČ.
Electronic supplementary material. Supplementary crystallographic data for this paper (including the selected212

interatomic distances, results of bond-valence analysis
and a CIF file) are available online at the Journal website(http://dx.doi.org/10.3190/jgeosci.241).

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